Ethylene copolymers are materials to which various vinyl-based comonomers have been introduced into the existing properties of LDPE (Low Density Polyethylene), and have been developed for various uses and are widely commercialized.
Ethylene copolymers are produced in a continuous process through free radical addition polymerization between ethylene monomers and vinyl-based comonomers in a high pressure reactor. Specifically, ethylene copolymers can be synthesized through chain-growth polymerization in which a free radical is formed from an initiator, and double bond monomers charged in excess are continuously reacted.
In the synthesis of an ethylene copolymer, the monomer and the initiator are charged in a high-pressure reactor, and reactants behave like a supercritical fluid under high pressure and are present with unreacted monomers. Through this polymerization, only about 15 to 30% of the monomers involved in the polymerization and the rest are recovered and reused.
Therefore, in order to increase the efficiency of the synthesis of an ethylene copolymer, it is necessary to effectively recover the unreacted monomers not involved in the polymerization reaction, and induce them to undergo a re-polymerization reaction. To this end, a variety of studies have been conducted on techniques in which, after the polymerization reaction, a mixture of unreacted monomers and copolymers is depressurized to separate unreacted monomers from the polymer, and the separated unreacted monomers are again compressed and charged in a high-pressure reactor.
However, there was still a limitation in that unreacted monomers are not sufficiently recovered from the final product. There was also a limitation in the process efficiency that a lot of cost was consumed in the compression process for charging the depressurized unreacted monomers in the high pressure reactor.
In this regard, there is a need to develop a new method for recovering unreacted monomers of an ethylene copolymer capable of realizing a low cost and high efficiency while exhibiting a greater improvement in the rate of recovery of unreacted monomers compared with a conventional one.